This invention relates to a magnetic bubble device and more particularly, to a magnetic bubble device having an improved magnetic bubble propagation characteristic and capable of being to operate stably over a wide range.
A magnetic bubble device generally comprises a replicate gate circuit, a transfer gate circuit and a bubble generator as its basic elements. A magnetic film for forming and holding therein magnetic bubbles is provided on a monocrystalline substrate and the basic elements are formed on the magnetic film via an insulating spacer. In such a magnetic bubble device, respective basic elements have laminated constructions. More particularly, a conductor pattern layer which passes a control current that controls (divides, propagates, generates, etc.) the magnetic bubbles, an insulating film, a propagation circuit pattern layer having magnetic bubble propagation path segments, and a passivation film are laminated in the order mentioned.
When one looks at a sectional contour of the laminated structure of the basic elements of a prior art magnetic bubble device, the insulating film comes in direct contact with the insulating spacer to cover a wide-area region of the spacer in which the conductor pattern segment does not exist, whereas in the presence of conductor pattern segments, the insulating film rises along the conductor pattern segment to cover the same. Since the insulating film has a uniform thickness, the propagation circuit pattern layer formed on the insulating film rises and lowers in conformity with the surface irregularity of the insulating film.
Considering the distance or spacing between the propagation path segment and the surface of the magnetic film containing magnetic bubbles, the spacing is small at the propagation path segment which is formed on a portion of the insulating film which comes in direct contact with the insulating spacer because of the absence of the conductor pattern segment, whereas the spacing is large at the propagation path segment which is formed on a raised portion of the insulating film due to the presence of the conductor pattern segment. Further, the propagation path segment which bridges adjacent raised portions of the insulating film by way of a valley of the insulating film whose bottom is in direct contact with the insulating spacer bears small, intermediate and large spacings with respect to the insulating spacer in accordance with bottom of the valley, slope of the valley and raised portion. In this manner, in the laminated structure of the prior art magnetic bubble device, the distance or spacing between the propagation path segment and the magnetic film containing the magnetic bubbles is not uniform. Generally speaking, as the spacing of the propagation path becomes different, the characteristic of the bubble propagation path for propagating the magnetic bubbles also becomes different.
The function of bias magnetic field upon the magnetic bubbles varies depending upon the distance of the propagation path from the magnetic film. If the function were too strong, the bubbles would disappear, whereas if the function were too weak, the bubble would be elongated so that they can no longer be called bubbles. For this reason, there exists a stable operation region of the bubble propagation path, and the stable operation region of the bubble propagation path, and the stable operation region of the bubble propagation path at a small distance and that of the bubble propagation path at a large distance do not coincide. Accordingly, a stable operation region common to these bubble propagation path segments is limited. In the propagation path segment bridging raised portions of the insulating film and which has a small distance, an intermediate distance and a large distance with respect to the insulating spacer, the distance changes rapidly between large and small values through the intermediate value so that the stable operation region which is common to the portions at large and small distances and the intermediate distance portion of the propagation path segment becomes narrow, thus limiting the stable operating region of the propagation path segment as a whole.